1CREATE FOREIGN TABLE(7) PostgreSQL 12.2 Documentation CREATE FOREIGN TABLE(7)
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6 CREATE_FOREIGN_TABLE - define a new foreign table
7
9 CREATE FOREIGN TABLE [ IF NOT EXISTS ] table_name ( [
10 { column_name data_type [ OPTIONS ( option 'value' [, ... ] ) ] [ COLLATE collation ] [ column_constraint [ ... ] ]
11 | table_constraint }
12 [, ... ]
13 ] )
14 [ INHERITS ( parent_table [, ... ] ) ]
15 SERVER server_name
16 [ OPTIONS ( option 'value' [, ... ] ) ]
17 CREATE FOREIGN TABLE [ IF NOT EXISTS ] table_name
19 PARTITION OF parent_table [ (
20 { column_name [ WITH OPTIONS ] [ column_constraint [ ... ] ]
21 | table_constraint }
22 [, ... ]
23 ) ] partition_bound_spec
24 SERVER server_name
25 [ OPTIONS ( option 'value' [, ... ] ) ]
26 where column_constraint is:
28 [ CONSTRAINT constraint_name ]
30 { NOT NULL |
31 NULL |
32 CHECK ( expression ) [ NO INHERIT ] |
33 DEFAULT default_expr |
34 GENERATED ALWAYS AS ( generation_expr ) STORED }
35 and table_constraint is:
37 [ CONSTRAINT constraint_name ]
39 CHECK ( expression ) [ NO INHERIT ]
40
42 CREATE FOREIGN TABLE creates a new foreign table in the current
43 database. The table will be owned by the user issuing the command.
44 If a schema name is given (for example, CREATE FOREIGN TABLE
46 myschema.mytable ...) then the table is created in the specified
47 schema. Otherwise it is created in the current schema. The name of the
48 foreign table must be distinct from the name of any other foreign
49 table, table, sequence, index, view, or materialized view in the same
50 schema.
51 CREATE FOREIGN TABLE also automatically creates a data type that
53 represents the composite type corresponding to one row of the foreign
54 table. Therefore, foreign tables cannot have the same name as any
55 existing data type in the same schema.
56 If PARTITION OF clause is specified then the table is created as a
58 partition of parent_table with specified bounds.
59 To be able to create a foreign table, you must have USAGE privilege on
61 the foreign server, as well as USAGE privilege on all column types used
62 in the table.
63
65 IF NOT EXISTS
66 Do not throw an error if a relation with the same name already
67 exists. A notice is issued in this case. Note that there is no
68 guarantee that the existing relation is anything like the one that
69 would have been created.
70 table_name
72 The name (optionally schema-qualified) of the table to be created.
73 column_name
75 The name of a column to be created in the new table.
76 data_type
78 The data type of the column. This can include array specifiers. For
79 more information on the data types supported by PostgreSQL, refer
80 to Chapter 8.
81 COLLATE collation
83 The COLLATE clause assigns a collation to the column (which must be
84 of a collatable data type). If not specified, the column data
85 type's default collation is used.
86 INHERITS ( parent_table [, ... ] )
88 The optional INHERITS clause specifies a list of tables from which
89 the new foreign table automatically inherits all columns. Parent
90 tables can be plain tables or foreign tables. See the similar form
91 of CREATE TABLE (CREATE_TABLE(7)) for more details.
92 PARTITION OF parent_table FOR VALUES partition_bound_spec
94 This form can be used to create the foreign table as partition of
95 the given parent table with specified partition bound values. See
96 the similar form of CREATE TABLE (CREATE_TABLE(7)) for more
97 details. Note that it is currently not allowed to create the
98 foreign table as a partition of the parent table if there are
99 UNIQUE indexes on the parent table. (See also ALTER TABLE ATTACH
100 PARTITION.)
101 CONSTRAINT constraint_name
103 An optional name for a column or table constraint. If the
104 constraint is violated, the constraint name is present in error
105 messages, so constraint names like col must be positive can be used
106 to communicate helpful constraint information to client
107 applications. (Double-quotes are needed to specify constraint names
108 that contain spaces.) If a constraint name is not specified, the
109 system generates a name.
110 NOT NULL
112 The column is not allowed to contain null values.
113 NULL
115 The column is allowed to contain null values. This is the default.
116 This clause is only provided for compatibility with non-standard
118 SQL databases. Its use is discouraged in new applications.
119 CHECK ( expression ) [ NO INHERIT ]
121 The CHECK clause specifies an expression producing a Boolean result
122 which each row in the foreign table is expected to satisfy; that
123 is, the expression should produce TRUE or UNKNOWN, never FALSE, for
124 all rows in the foreign table. A check constraint specified as a
125 column constraint should reference that column's value only, while
126 an expression appearing in a table constraint can reference
127 multiple columns.
128 Currently, CHECK expressions cannot contain subqueries nor refer to
130 variables other than columns of the current row. The system column
131 tableoid may be referenced, but not any other system column.
132 A constraint marked with NO INHERIT will not propagate to child
134 tables.
135 DEFAULT default_expr
137 The DEFAULT clause assigns a default data value for the column
138 whose column definition it appears within. The value is any
139 variable-free expression (subqueries and cross-references to other
140 columns in the current table are not allowed). The data type of the
141 default expression must match the data type of the column.
142 The default expression will be used in any insert operation that
144 does not specify a value for the column. If there is no default for
145 a column, then the default is null.
146 GENERATED ALWAYS AS ( generation_expr ) STORED
148 This clause creates the column as a generated column. The column
149 cannot be written to, and when read the result of the specified
150 expression will be returned.
151 The keyword STORED is required to signify that the column will be
153 computed on write. (The computed value will be presented to the
154 foreign-data wrapper for storage and must be returned on reading.)
155 The generation expression can refer to other columns in the table,
157 but not other generated columns. Any functions and operators used
158 must be immutable. References to other tables are not allowed.
159 server_name
161 The name of an existing foreign server to use for the foreign
162 table. For details on defining a server, see CREATE SERVER
163 (CREATE_SERVER(7)).
164 OPTIONS ( option 'value' [, ...] )
166 Options to be associated with the new foreign table or one of its
167 columns. The allowed option names and values are specific to each
168 foreign data wrapper and are validated using the foreign-data
169 wrapper's validator function. Duplicate option names are not
170 allowed (although it's OK for a table option and a column option to
171 have the same name).
172
174 Constraints on foreign tables (such as CHECK or NOT NULL clauses) are
175 not enforced by the core PostgreSQL system, and most foreign data
176 wrappers do not attempt to enforce them either; that is, the constraint
177 is simply assumed to hold true. There would be little point in such
178 enforcement since it would only apply to rows inserted or updated via
179 the foreign table, and not to rows modified by other means, such as
180 directly on the remote server. Instead, a constraint attached to a
181 foreign table should represent a constraint that is being enforced by
182 the remote server.
183 Some special-purpose foreign data wrappers might be the only access
185 mechanism for the data they access, and in that case it might be
186 appropriate for the foreign data wrapper itself to perform constraint
187 enforcement. But you should not assume that a wrapper does that unless
188 its documentation says so.
189 Although PostgreSQL does not attempt to enforce constraints on foreign
191 tables, it does assume that they are correct for purposes of query
192 optimization. If there are rows visible in the foreign table that do
193 not satisfy a declared constraint, queries on the table might produce
194 incorrect answers. It is the user's responsibility to ensure that the
195 constraint definition matches reality.
196 Similar considerations apply to generated columns. Stored generated
198 columns are computed on insert or update on the local PostgreSQL server
199 and handed to the foreign-data wrapper for writing out to the foreign
200 data store, but it is not enforced that a query of the foreign table
201 returns values for stored generated columns that are consistent with
202 the generation expression. Again, this might result in incorrect query
203 results.
204 While rows can be moved from local partitions to a foreign-table
206 partition (provided the foreign data wrapper supports tuple routing),
207 they cannot be moved from a foreign-table partition to another
208 partition.
209
211 Create foreign table films, which will be accessed through the server
212 film_server:
213 CREATE FOREIGN TABLE films (
215 code char(5) NOT NULL,
216 title varchar(40) NOT NULL,
217 did integer NOT NULL,
218 date_prod date,
219 kind varchar(10),
220 len interval hour to minute
221 )
222 SERVER film_server;
223 Create foreign table measurement_y2016m07, which will be accessed
225 through the server server_07, as a partition of the range partitioned
226 table measurement:
227 CREATE FOREIGN TABLE measurement_y2016m07
229 PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO ('2016-08-01')
230 SERVER server_07;
231
233 The CREATE FOREIGN TABLE command largely conforms to the SQL standard;
234 however, much as with CREATE TABLE, NULL constraints and zero-column
235 foreign tables are permitted. The ability to specify column default
236 values is also a PostgreSQL extension. Table inheritance, in the form
237 defined by PostgreSQL, is nonstandard.
238
240 ALTER FOREIGN TABLE (ALTER_FOREIGN_TABLE(7)), DROP FOREIGN TABLE
241 (DROP_FOREIGN_TABLE(7)), CREATE TABLE (CREATE_TABLE(7)), CREATE SERVER
242 (CREATE_SERVER(7)), IMPORT FOREIGN SCHEMA (IMPORT_FOREIGN_SCHEMA(7))
243PostgreSQL 12.2 2020 CREATE FOREIGN TABLE(7)